The present invention relates to a polyurethane composition with adjustable mix viscosity, to a polyurethane geotextile composite prepared with such polyurethane composition and a process for producing such polyurethane geotextile composites.
In recent years, the management of natural resources has become important in many countries throughout the world. Efforts have been directed both toward the conservation of our resources and toward the elimination of pollution from our environment. Particular emphasis has been placed on waste leakage and water loss.
Losses in the distribution of water using unlined irrigation ditches are estimated at a minimum to be 25% and in some situations to be more than 50% depending upon the porosity of the ditch surface and the distance the water is being moved. In most rural areas, ditches are formed by excavating the soil to the desired depth and width. The water moves through the ditch in contact with the exposed natural surface. This can be sand, clay, rocks, etc. and, more commonly, mixtures thereof. The porosity will depend upon the proportions of the different components.
The loss of water in unlined irrigation ditches at one time was considered acceptable only because the supply of water exceeded demand. However, as civilization has developed and world population has increased, more water is required for both greater food production and for the markedly increasing non-agriculture uses. In addition to greater domestic uses in sanitation, industry now employs large quantities of water in manufacturing and processing procedures.
This high level of consumption plus the very high cost of developing new water supplies has shifted attention to water conservation. Domestic appliances that use less water have been developed. Also, industry has installed recycling purification systems to reduce water consumption.
Although conservation efforts have reduced water consumption to a degree, water is still in relatively short supply, particularly in recent years with the severe droughts in the United States and other countries. Since the most cost effective conservation opportunities and readily accessible water supplies have already been developed, greater attention must be directed to improving the efficiency of water distribution systems.
Improvements in water distribution have been made. A limited number of ditches and canals have been lined with concrete and/or preformed concrete pipes. Concrete is durable and has a long life when properly used. However, concrete is expensive to place and finish and is damaged by unfavorable temperatures during curing. Also, concrete is subject to frost damage, cracking and heaving which results in leaks.
Processes for forming composite liners for canals and ditches and apparatus to perform such a processes are disclosed, for example, in U.S. Pat. Nos. 4,872,784; 4,955,759; 4,955,760; 5,049,006; 5,062,740; and 5,421,677.
However, the above noted patents give almost no guidance as to solidifiable compositions which should be used. For example, U.S. Pat. No. 4,872,784 (at column 5, lines 55-60), U.S. Pat. No. 4,955,759 (at column 5, lines 58-63), U.S. Pat. No. 4,955,760 (at column 4, lines 55-60) and U.S. Pat. No. 5,062,740 (at column 4, lines 56-61) each broadly suggest the use of a foamed polyurethane resin without disclosing any specific formulations. U.S. Pat. No. 5,049,006 (at column 4, lines 26-32) and U.S. Pat. No. 5,145,282 (at column 5, line 64-column 6, line 2) broadly suggest use of a thermosetting resin forming mixture such as a polyester or a polyurethane forming mixture, without describing any specific formulations.
U.S. Pat. No. 5,421,677 (xe2x80x9cthe ""677 patentxe2x80x9d) which is directed to an improved process of forming a ditch liner discloses the use of a mixture composed of one or more polyisocyanates, a polyol mixture, one or more fillers, and a catalyst. The mixture of the ""677 patent is dispensed on a geotextile, thereby forming a liquid polyurethane impregnated geotextile composite. The liquid polyurethane impregnated geotextile composite is then placed over the surface of an area to be lined and allowed to cure, thereby forming a polyurethane/geotextile composite. The mixture disclosed in the ""677 patent cures in a reasonable amount of time and under varying temperature conditions. However, the viscosity of that mixture varies widely.
More specifically, at high temperatures (e.g., 30xc2x0-50xc2x0 C.), the mixture of the ""677 patent has an extremely low viscosity. In a ditch liner application, such a low viscosity mixture will tend to flow to the bottom of the ditch. As a result, an uneven ditch liner having very little binder to adhere to the substrate and protect the top of the ditch from seepage is formed. Excess binder settles on the bottom of the ditch. When thick layers of the still liquid polyurethane are formed on the bottom of a ditch, those layers have a tendency to foam under humid conditions. Such foaming weakens the liner by reducing water impermeability.
For the foregoing reasons, it would be desirable to develop a polyurethane composition the viscosity of which may be readily adjusted to obtain optimum performance even when the temperature and humidity at the site where it is being used are not constant. Specifically, a polyurethane composition that maintains the desirable low viscosity of the starting materials but also has a mix viscosity that can be increased to a level such that run off on vertical surfaces is avoided would be advantageous. Additionally, it would be desirable to develop a composite made with such a polyurethane composition, so that a ditch lined with the composite will be sufficiently protected at the outer edges that seepage is substantially avoided and no excess polyurethane composition will settle on the bottom of the ditch.
The invention is directed toward a polyurethane composition formed from a reaction mixture characterized by an adjustable viscosity which reaction mixture comprises:
a) a liquid polyisocyanate having an isocyanate group content of at least 10% by weight;
b) an isocyanate reactive component comprising a polyether polyol having from 2-6 hydroxyl groups and a number average molecular weight of from at least 250 to about 8,000 and 0 to 10% by weight, based on total weight of b), of a low molecular weight (i.e., number average molecular weight less than 250) diol or triol having a hydroxy equivalent weight from about 31 to 99,
c) a catalyst for catalyzing the reaction between hydroxyl groups and isocyanate groups;
d) from 0.2 to about 5.0 parts by weight per hundred parts by weight of component b) of a viscosity adjusting material such as a diamine, a polyamine, or an amine-terminated polyol; and optionally,
(e) a filler.
The invention is further directed to the polyurethane-forming reaction mixture characterized by adjustable viscosity, a polyurethane geotextile composite produced with such an adjustable polyurethane-forming reaction mixture, a process for producing such composites, and to a process for lining a ditch or canal with such a composite.
The polyurethane-forming reaction mixture characterized by adjustable mix viscosity remains flowable during application, e.g., while it is being applied to a substrate. By xe2x80x9cflowablexe2x80x9d, it is meant that the polyurethane-forming composition with adjustable mix viscosity is still a self leveling liquid having a viscosity low enough to be applied evenly on a substrate such as a geotextile, but also high enough that after it is applied to the substrate, run-off on vertical surfaces such as those of a ditch and/or canal is avoided.
The amount of the viscosity-adjusting compound included in the polyurethane-forming mixture is increased with increasing temperature and lowered at lower temperature to achieve the desirable mix viscosity at any application temperature without any noticeable shortening of the gel time. These and other advantages of the present invention will become better understood by the following description and appended claims.